Subject of the present invention is a system for reducing the seismic load of tall buildings with high centre of gravity, and to prevent the tipping over of building provided with elastic elements between the foundation and the superstucture.
It is generally known that the various buildings are exposed to seismic loads when accelerating motions occur in parts of the building acted upon the effects of seismic shocks.
One way of reducing the seismic forces is the reduction of the mass of the buildings, significant results were accomplished in this area with the developments in the architecture field.
Another possible method of reducing the seismic forces is providing an intermediate system between the building foundation and the superstucture, which is suitable for absorption of the energy produced during the seismic shocks. The various methods for reduction of the seismic load essentially follow this pattern.
It is known to build in horizontal wall reinforcements between the foundation and the upper wall surface, which break up in the wake of the seismic motion, and the so produced deformations absorb a certain part of the energy. These walls are constructed by using mortar for joining the building units suitable to withstand extreme deformations.
In some cases energy-absorbing paddings are installed between the foundation and the superstructure, as well as between the foundation and the ground. Rollers of limited motion are installed between the foundation and the superstructure. Sliding panels made of synthetic material are arranged between the foundation and the ground according to one of these methods.
In other cases, steel elements withstanding the torsional and longitudinal deformations are built in between the ground and the building foundation.
Sometimes, sandwich type rubber springs are installed between the building foundation and the superstructure.
The energy may be absorbed by the deformation of reinforced concrete pillars as well. Again according to another method so-called disengaging joints are built in on the ground floor of the building. These are characterized in that they become ruined in case of forces exceeding the specified limit force thus preventing the development of the excessive horizontal accelerations and their transfer to the superstructure.
Different shock absorbers are described in the Swiss Pat. No. 584 333 and in the U.S. Pat. No. 394,895.
According to another method see for instance the European patent application No. 005 6258, a spring system is built in between the foundation and the superstructure, which enables the development of seismic forces equivalent maximally to the horizontal forces developed from the wind load. In case of more intensive forces the spring system yields, consequently becoming automatically unsuitable for the transfer of higher forces as a result of its own plastic deformation. The spring system includes a motion-damping part of high elastic deformation capacity, and a highly effective plastic energy-absorbing part. The motion-damping part is formed as a set of steel mandrels extending into the surfaces of the foundation and the superstructure facing each other, and these steel mandrels are unsuitable for absorption of the loads higher than those developed from the maximal wind load.
All these methods are based on building in the energy-absorbing elastic elements between the foundation and the meaming that the foundation and the superstructure are separated from each other so that the foundation is capable of moving in a horizontal direction in relation to the superstructure.
These methods eliminate by necessity or at least reduce considerably the connection ensuring the vertical cementing, anchoring force between the foundation and the superstructure.
In view of the fact that the resultant of the horizontal seismic forces produced by the seismic acceleration reacts in the centre of the building, it depends on the proportions of the building whether it results in a tipping over effect. In case of towery buildings with high centre of gravity this problem is significant, because the elastic connections serving the absorption of the seismic forces reduce the stability of the anchorage.